Integrated circuits may be formed using various photolithographic techniques. Such techniques are used to form different types of components and devices including transistors. One type of transistor is a Metal Oxide Semiconductor Field Effect Transistor (MOSFET). MOSFET devices use a gate terminal, a source terminal, and a drain terminal. Among other functions, the MOSFET device may act as a switch. When acting as a switch, the signal applied to the gate terminal will either cause the MOSFET device to allow or prohibit current flow between the source and drain terminals.
The source and drain components of a MOSFET device typically include doped regions of a semiconductor substrate or material. The channel between the source and drain regions underneath a gate device may be shaped like a fin that passes through the bottom portion of the gate structure in a perpendicular manner. Transistors that use fin shaped channels are sometimes referred to as finFETs.
In some cases, it can be beneficial to introduce a strain into the fin structures. Straining may be done by injecting a type of semiconductor with a different lattice constant than the original semiconductor material. For example, a silicon fin may be doped with silicon-germanium. This will cause a strain in the crystalline structure of the fin. If done properly, this can increase carrier mobility and thus increase the efficiency of the fin. This straining process, however, can be harmed by various processes such as thermal annealing. Thermal annealing is part of forming source and drain regions. It is desirable form strained structures that will not be adversely affected by various processes such as thermal annealing.